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• Obstacle Avoidance steering behavior: how can an entity avoid an obstacle while other forces are acting on the entity?

  - by Prog

  I'm trying to implement the Obstacle Avoidance steering behavior in my 2D game. Currently my approach is to apply a force on the entity, in the direction of the normal of the heading, scaled by a number that gets bigger the closer we are to the obstacle. This is supposed to push the entity to the side and avoid the obstacle that blocks it's way. However, in the same time that my entity tries to avoid an obstacle, it Seeks to a point more or less behind the obstacle (which is the reason it needs to avoid the obstacle in the first place). The Seek algorithm constantly applies a force on the entity that pushes it (more or less) in the direction of the obstacle, while the Obstacle Avoidance algorithm constantly applies a force that pushes the entity away (more accurately, to the side) of the obstacle. The result is that sometimes the entity succesfully avoids the obstacle, and sometimes it collides with it, depending on the strength of the avoidance force I'm applying. How can I make sure that a force will succeed in steering the entity in some direction, while other forces are currently acting on the entity? (And while still looking natural). I can't allow entities to collide with obstacles when realistically they should be able to easily avoid them, doesn't matter what they're currently doing. Also, the Obstacle Avoidance algorithm is made exactly for the case where another force is acting on the entity. Otherwise it wouldn't be moving and there would be no need to avoid anything. So maybe I'm missing something. Thanks

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• How to safely copy an object?

  - by Prog

  This question is going to be a little long. Please bear with me. Something that happened in a project of mine made me think about how to safely copy objects. I'll present the situation I had and then ask a question. There was a class SomeClass: class SomeClass{ Thing[] things; public SomeClass(Thing[] things){ this.things = things; } // irrelevant stuff omitted public SomeClass copy(){ return new SomeClass(things); } } There was another class Processor that takes SomeClass objects, copies them (via someClassInstance.copy()), manipulates the copy's state, and returns the copy. Here it is: class Processor{ public SomeClass processObject(SomeClass object){ SomeClass copy = object.copy(); manipulateTheCopy(copy); return copy; } // irrelevant stuff omitted } I ran this, and it had bugs. I looked into these bugs, and it turned out that the manipulations Processor does on copy actually affect not only the copy, but also the original SomeClass object that was passed into processObject. I found out that it was because the original and the copy shared state - because the original passed it's field things into the copy when creating it. This made me realize that copying objects is harder than simply instantiating them with the same fields as the original. For the two objects to be completely disconnected, without any shared state, each of the fields passed to the copy also has to be copied. And if that object contains other objects - they have to be copied too. And so on. So basically, in order to be able to actually copy an object, each class in the system must have a copy() method, that also invokes copy() on all of it's fields, and so on. So for example, for copy() in SomeClass to work, it needs to look like this: public SomeClass copy(){ Thing[] copyThings = new Thing[things.length]; for(int i=0; i<things.length; i++) copyThings[i] = things[i].copy(); return new SomeClass(copyThings); } And if Thing has object fields of it's own, than it's own copy() method must be appropriate: class Thing{ Apple apple; Pencil pencil; int number; public Thing(Apple apple, Pencil pencil, int number){ this.apple = apple; this.pencil = pencil; this.number = number; } public Thing copy(){ // 'number' is a primitve. return new Thing(apple.getCopy(), pencil.getCopy(), number); } } And so on. Of course, instead of all classes having a copy() method, the copying mechanism can happen in all of the getters and the constructors of classes (unless places where it isn't suitable, for example when the field points to an external object, not to an object that 'is part' of this object). Still, that means that in order to be able to safely copy an object - most classes would have to have copying mechanisms in their getters. My question is divided into two parts: How frequently do you need to get a copy of an object? Is this a regular issue? Is the technique described common and/or reasonable? Or is there a better way to make safe copies of objects? Or is there an easier way to safely copy objects, without them sharing any state?

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• Are first-class functions a substitute for the Strategy pattern?

  - by Prog

  The Strategy design pattern is often regarded as a substitute for first-class functions in languages that lack them. So for example say you wanted to pass functionality into an object. In Java you'd have to pass in the object another object which encapsulates the desired behavior. In a language such as Ruby, you'd just pass the functionality itself in the form of an annonymous function. However I was thinking about it and decided that maybe Strategy offers more than a plain annonymous function does. This is because an object can hold state that exists independently of the period when it's method runs. However an annonymous function by itself can only hold state that ceases to exist the moment the function finishes execution. So my question is: when using a language that features first-class functions, would you ever use the Strategy pattern (i.e. encapsulate the functionality you want to pass around in an explicit object), or would you always use an annonymous function? When would you decide to use Strategy when you can use a first-class function?

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• Is there a way to avoid type-checking in this scenario?

  - by Prog

  I have a class SuperClass with two subclasses SubClassA and SubClassB. I have a method in a different class which takes a SuperClass parameter. The method should do different things depending on the type of the object it receives. To illustrate: public void doStuff(SuperClass object){ // if the object is of type SubClassA, do something. // if it's of type SubClassB, do something else. } I want to avoid type-checking (i.e. instanceof) because it doesn't feel like proper OO design. But I can't figure out how to employ Polymorphism to elegantly solve this problem. How can I solve this problem elegantly?

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• AI agents with FSM: a question regarding this

  - by Prog

  Finite State Machines implemented with the State design pattern are a common way to design AI agents. I am familiar with the State design pattern and know how to implement it. However I have a question regarding how this is used in games to design AI agents. Please consider a class Monster that represents an AI agent. Simplified it looks like this: class Monster{ State state; // other fields omitted public void update(){ // called every game-loop cycle state.execute(this); } public void setState(State state){ this.state = state; } // irrelevant stuff omitted } There are several State subclasses that implement execute() differently. So far classic State pattern. Here's my question: AI agents are subject to environmental effects and other objects communicating with them. For example an AI agent might tell another AI agent to attack (i.e. agent.attack()). Or a fireball might tell an AI agent to fall down. This means that the agent must have methods such as attack() and fallDown(), or commonly some message receiving mechanism to understand such messages. My question is divided to two parts: 1- Please say if this is correct: With an FSM, the current State of the agent should be the one taking care of such method calls - i.e. the agent delegates to the current state upon every event. Correct? Or wrong? 2- If correct, than how is this done? Are all states obligated by their superclass) to implement methods such as attack(), fallDown() etc., so the agent can always delegate to them on almost every event? Or is it done in some other way?

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• Must all AI states be able to react to any event?

  - by Prog

  FSMs implemented with the State design pattern are a common way to design AI agents. I am familiar with the State design pattern and know how to implement it. How is this used in games to design AI agents? Consider a simplified class Monster, representing an AI agent: class Monster { State state; // other fields omitted public void update(){ // called every game-loop cycle state.execute(this); } public void setState(State state){ this.state = state; } // irrelevant stuff omitted } There are several State subclasses implementing execute() differently. So far, classic State pattern. AI agents are subject to environmental effects and other objects communicating with them. For example, an AI agent might tell another AI agent to attack (i.e. agent.attack()). Or a fireball might tell an AI agent to fall down. This means that the agent must have methods such as attack() and fallDown(), or commonly some message receiving mechanism to understand such messages. With an FSM, the current State of the agent should be the one taking care of such method calls - i.e. the agent delegates to the current state upon every event. Is this correct? If correct, how is this done? Are all states obligated by their superclass to implement methods such as attack(), fallDown() etc., so the agent can always delegate to them on almost every event? Or is it done in some other way?

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• Updating entities in response to collisions - should this be in the collision-detection class or in the entity-updater class?

  - by Prog

  In a game I'm working on, there's a class responsible for collision detection. It's method detectCollisions(List<Entity> entities) is called from the main gameloop. The code to update the entities (i.e. where the entities 'act': update their positions, invoke AI, etc) is in a different class, in the method updateEntities(List<Entity> entities). Also called from the gameloop, after the collision detection. When there's a collision between two entities, usually something needs to be done. For example, zero the velocity of both entities in the collision, or kill one of the entities. It would be easy to have this code in the CollisionDetector class. E.g. in psuedocode: for(Entity entityA in entities){ for(Entity entityB in entities){ if(collision(entityA, entityB)){ if(entityA instanceof Robot && entityB instanceof Robot){ entityA.setVelocity(0,0); entityB.setVelocity(0,0); } if(entityA instanceof Missile || entityB instanceof Missile){ entityA.die(); entityB.die(); } } } } However, I'm not sure if updating the state of entities in response to collision should be the job of CollisionDetector. Maybe it should be the job of EntityUpdater, which runs after the collision detection in the gameloop. Is it okay to have the code responding to collisions in the collision detection system? Or should the collision detection class only detect collisions, report them to some other class and have that class affect the state of the entities?

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• Java desktop programmer starting to learn Android development: how different is it?

  - by Prog

  I'm a Java programmer. All of my experience is on desktop applications, using Swing for the GUI. I spend a lot of time studying OOP, I have decent understanding of OO concepts and I design and program by the OO approach. I'm thinking of starting to learn Android development soon, and I'm wondering how different it is from desktop development. Obviously the GUI libraries will be different (not Swing), but other than that, I want to know if there are significant differences. I will divide this question to two parts: Apart from the GUI libraries, am I still going to use the standard Java libarary I'm used to? Aka same data structues, same utility classes, etc.? If not, what are the main differences between the libraries I'm used to and the libraries I'll be using? How different is Android development in regard to OO design? Are all of the familiar principles, design patterns, techniques and best pratices just as valid and used? Or is OOP and OOD in Android development significantly different than OO in desktop development? To summarize: apart from GUI design, how different is Java Android development than Java desktop development?

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• Do threads delete themselves?

  - by Prog

  Let's say I was working on a Swing application. Most of it is run on the EDT using SwingUtilities.invokeLater() inside the main method, because I heard (please correct me if I'm wrong) that that's what you need to do with Swing. However, some parts of it shouldn't run on the EDT. These parts are parts that take long to complete (I assume that this is because long tasks on the EDT will interfere with GUI stuff the EDT should be doing, and thus these kinds of tasks should be run on parallel, on a different thread. Is this assumption correct?) To do this, when I need to perform a task that takes long to complete and thus can't be run on the EDT like the rest of the program, I create a new thread and run that task inside it. My question is: When the run() method of that new thread finishes, aka the thread finished it's job. Does it delete itself? Or does it keep existing in the memory?

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• Why do VMs need to be "stack machines" or "register machines" etc.?

  - by Prog

  (This is an extremely newbie-ish question). I've been studying a little about Virtual Machines. Turns out a lot of them are designed very similarly to physical or theoretical computers. I read that the JVM for example, is a 'stack machine'. What that means (and correct me if I'm wrong) is that it stores all of it's 'temporary memory' on a stack, and makes operations on this stack for all of it's opcodes. For example, the source code 2 + 3 will be translated to bytecode similar to: push 2 push 3 add My question is this: JVMs are probably written using C/C++ and such. If so, why doesn't the JVM execute the following C code: 2 + 3..? I mean, why does it need a stack, or in other VMs 'registers' - like in a physical computer? The underlying physical CPU takes care of all of this. Why don't VM writers simply execute the interpreted bytecode with 'usual' instructions in the language the VM is programmed with? Why do VMs need to emulate hardware, when the actual hardware already does this for us? Again, very newbie-ish questions. Thanks for your help

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• Should I always encapsulate an internal data structure entirely?

  - by Prog

  Please consider this class: class ClassA{ private Thing[] things; // stores data // stuff omitted public Thing[] getThings(){ return things; } } This class exposes the array it uses to store data, to any client code interested. I did this in an app I'm working on. I had a ChordProgression class that stores a sequence of Chords (and does some other things). It had a Chord[] getChords() method that returned the array of chords. When the data structure had to change (from an array to an ArrayList), all client code broke. This made me think - maybe the following approach is better: class ClassA{ private Thing[] things; // stores data // stuff omitted public Thing[] getThing(int index){ return things[index]; } public int getDataSize(){ return things.length; } public void setThing(int index, Thing thing){ things[index] = thing; } } Instead of exposing the data structure itself, all of the operations offered by the data structure are now offered directly by the class enclosing it, using public methods that delegate to the data structure. When the data structure changes, only these methods have to change - but after they do, all client code still works. Note that collections more complex than arrays might require the enclosing class to implement even more than three methods just to access the internal data structure. Is this approach common? What do you think of this? What downsides does it have other? Is it reasonable to have the enclosing class implement at least three public methods just to delegate to the inner data structure?

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• "Default approach" when creating a class from scratch: getters for everything, or limited access?

  - by Prog

  Until recently I always had getters (and sometimes setters but not always) for all the fields in my class. It was my 'default': very automatic and I never doubted it. However recently some discussions on this site made me realize maybe it's not the best approach. When you create a class, you often don't know exactly how it's going to be used in the future by other classes. So in that sense, it's good to have getters and setter for all of the fields in the class. So other classes could use it in the future any way they want. Allowing this flexibility doesn't require you to over engineer anything, only to provide getters. However some would say it's better to limit the access to a class, and only allow access to certain fields, while other fields stay completely private. What is your 'default' approach when building a class from scratch? Do you make getters for all the fields? Or do you always choose selectively which fields to expose through a getter and which to keep completely private?

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• Advice on approaching a significant rearrangement/refactoring?

  - by Prog

  I'm working on an application (hobby project, solo programmer, small-medium size), and I have recently redesigned a significant part of it. The program already works in it's current state, but I decided to reimplement things to improve the OO design. I'm about to implement this new design by refactoring a big part of the application. Thing is I'm not sure where to start. Obviously, by the nature of a rearrangement, the moment you change one part of the program several other parts (at least temporarily) break. So it's a little 'scary' to rearrange something in a piece of software that already works. I'm asking for advice or some general guidelines: how should I approach a significant refactoring? When you approach rearranging large parts of your application, where do you start? Note that I'm interested only in re-arranging the high-level structure of the app. I have no intention of rewriting local algorithms.

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• "Collection Wrapper" pattern - is this common?

  - by Prog

  A different question of mine had to do with encapsulating member data structures inside classes. In order to understand this question better please read that question and look at the approach discussed. One of the guys who answered that question said that the approach is good, but if I understood him correctly - he said that there should be a class existing just for the purpose of wrapping the collection, instead of an ordinary class offering a number of public methods just to access the member collection. For example, instead of this: class SomeClass{ // downright exposing the concrete collection. Things[] someCollection; // other stuff omitted Thing[] getCollection(){return someCollection;} } Or this: class SomeClass{ // encapsulating the collection, but inflating the class' public interface. Thing[] someCollection; // class functionality omitted. public Thing getThing(int index){ return someCollection[index]; } public int getSize(){ return someCollection.length; } public void setThing(int index, Thing thing){ someCollection[index] = thing; } public void removeThing(int index){ someCollection[index] = null; } } We'll have this: // encapsulating the collection - in a different class, dedicated to this. class SomeClass{ CollectionWrapper someCollection; CollectionWrapper getCollection(){return someCollection;} } class CollectionWrapper{ Thing[] someCollection; public Thing getThing(int index){ return someCollection[index]; } public int getSize(){ return someCollection.length; } public void setThing(int index, Thing thing){ someCollection[index] = thing; } public void removeThing(int index){ someCollection[index] = null; } } This way, the inner data structure in SomeClass can change without affecting client code, and without forcing SomeClass to offer a lot of public methods just to access the inner collection. CollectionWrapper does this instead. E.g. if the collection changes from an array to a List, the internal implementation of CollectionWrapper changes, but client code stays the same. Also, the CollectionWrapper can hide certain things from the client code - from example, it can disallow mutation to the collection by not having the methods setThing and removeThing. This approach to decoupling client code from the concrete data structure seems IMHO pretty good. Is this approach common? What are it's downfalls? Is this used in practice?

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• Writing a method to 'transform' an immutable object: how should I approach this?

  - by Prog

  (While this question has to do with a concrete coding dilemma, it's mostly about what's the best way to design a function.) I'm writing a method that should take two Color objects, and gradually transform the first Color into the second one, creating an animation. The method will be in a utility class. My problem is that Color is an immutable object. That means that I can't do color.setRGB or color.setBlue inside a loop in the method. What I can do, is instantiate a new Color and return it from the method. But then I won't be able to gradually change the color. So I thought of three possible solutions: 1- The client code includes the method call inside a loop. For example: int duration = 1500; // duration of the animation in milliseconds int steps = 20; // how many 'cycles' the animation will take for(int i=0; i<steps; i++) color = transformColor(color, targetColor, duration, steps); And the method would look like this: Color transformColor(Color original, Color target, int duration, int steps){ int redDiff = target.getRed() - original.getRed(); int redAddition = redDiff / steps; int newRed = original.getRed() + redAddition; // same for green and blue .. Thread.sleep(duration / STEPS); // exception handling omitted return new Color(newRed, newGreen, newBlue); } The disadvantage of this approach is that the client code has to "do part of the method's job" and include a for loop. The method doesn't do it's work entirely on it's own, which I don't like. 2- Make a mutable Color subclass with methods such as setRed, and pass objects of this class into transformColor. Then it could look something like this: void transformColor(MutableColor original, Color target, int duration){ final int STEPS = 20; int redDiff = target.getRed() - original.getRed(); int redAddition = redDiff / steps; int newRed = original.getRed() + redAddition; // same for green and blue .. for(int i=0; i<STEPS; i++){ original.setRed(original.getRed() + redAddition); // same for green and blue .. Thread.sleep(duration / STEPS); // exception handling omitted } } Then the calling code would usually look something like this: // The method will usually transform colors of JComponents JComponent someComponent = ... ; // setting the Color in JComponent to be a MutableColor Color mutableColor = new MutableColor(someComponent.getForeground()); someComponent.setForeground(mutableColor); // later, transforming the Color in the JComponent transformColor((MutableColor)someComponent.getForeground(), new Color(200,100,150), 2000); The disadvantage is - the need to create a new class MutableColor, and also the need to do casting. 3- Pass into the method the actual mutable object that holds the color. Then the method could do object.setColor or similar every iteration of the loop. Two disadvantages: A- Not so elegant. Passing in the object that holds the color just to transform the color feels unnatural. B- While most of the time this method will be used to transform colors inside JComponent objects, other kinds of objects may have colors too. So the method would need to be overloaded to receive other types, or receive Objects and have instanceof checks inside.. Not optimal. Right now I think I like solution #2 the most, than solution #1 and solution #3 the least. However I'd like to hear your opinions and suggestions regarding this.

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• Significant amount of the time, I can't think of a reason to have an object instead of a static class. Do objects have more benefits than I think?

  - by Prog

  I understand the concept of an object, and as a Java programmer I feel the OO paradigm comes rather naturally to me in practice. However recently I found myself thinking: Wait a second, what are actually the practical benefits of using an object over using a static class (with proper encapsulation and OO practices)? I could think of two benefits of using an object (both significant and powerful): Polymorphism: allows you to swap functionality dynamically and flexibly during runtime. Also allows to add new functionality 'parts' and alternatives to the system easily. For example if there's a Car class designed to work with Engine objects, and you want to add a new Engine to the system that the Car can use, you can create a new Engine subclass and simply pass an object of this class into the Car object, without having to change anything about Car. And you can decide to do so during runtime. Being able to 'pass functionality around': you can pass an object around the system dynamically. But are there any more advantages to objects over static classes? Often when I add new 'parts' to a system, I do so by creating a new class and instantiating objects from it. But recently when I stopped and thought about it, I realized that a static class would do just the same as an object, in a lot of the places where I normally use an object. For example, I'm working on adding a save/load-file mechanism to my app. With an object, the calling line of code will look like this: Thing thing = fileLoader.load(file); With a static class, it would look like this: Thing thing = FileLoader.load(file); What's the difference? Fairly often I just can't think of a reason to instantiate an object when a plain-old static-class would act just the same. But in OO systems, static classes are fairly rare. So I must be missing something. Are there any more advantages to objects other from the two that I listed? Please explain.

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• How to avoid tons of `instanceof` in collision detection?

  - by Prog

  Consider a simple game with 4 kinds of entities: Robots, Dogs, Missiles, Walls. Here's a simple collision-detection mechanism in psuedocode: (I know, O(n^2). Irrelevant for this question). for(Entity entityA in entities){ for(Entity entityB in entities){ if(collision(entityA, entityB)){ if(entityA instanceof Robot && entityB instanceof Dog) entityB.die(); if(entityA instanceof Robot && entityB instanceof Missile){ entityA.die(); entityB.die(); } if(entityA instanceof Missile && entityB instanceof Wall) entityB.die(); // .. and so on } } } Obviously this is very ugly, and will get bigger and harder to maintain the more entities there are, and the more conditions there are. One option to make this better is to have separate lists for each kind of entity. For example a Robots list, a Dogs list etc. And than check for collisions of all Robots with Dogs, and all Dogs with Walls, etc. This is better, but I still don't think it's good. So my question is: The collision detection system spotted a collision. Now what? What is the common way to react to the collision? Should the system notify the entity itself that it collided with something, and have it decide for itself how to react? E.g. entityA.reactToCollision(entityB). Or is there some other solution?

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• We say Reference are const pointers. Why I am able to assign a new variable to ref B? The below prog

  - by sandeep

  #include<iostream.h> int main() { int a=10; int &b=a; cout<<"B"<<'\n'<<b; cout<<"A"<<'\n'<<a; b=100; cout<<"B"<<'\n'<<b; cout<<"A"<<'\n'<<a; int c=20; b=c; cout<<"C"<<'\n'<<c; cout<<"B"<<'\n'<<b; }

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• Bash arrays and case statements - review my script

  - by Felipe Alvarez

  #!/bin/bash # Change the environment in which you are currently working. # Actually, it calls the relevant 'lettus.sh' script if [ "${BASH_SOURCE[0]}" == "$0" ]; then echo "Try running this as \". chenv $1\"" exit 0 fi usage(){ echo "Usage: . ${PROG} -- Shows a list of user-selectable environments." echo " . ${PROG} [env] -- Select environment." echo " . ${PROG} -h -- Shows this usage screen." return } showEnv(){ # check if index0 exists, assume we have at least the first (zeroth) element #if [ -z "${envList}" ]; then if [ -z "${envList[0]}" ]; then echo "array \$envList is empty! " >&2 return 1 fi # Show all elements in array (0 -> n-1) for i in $(seq 0 $((${#envList[@]} - 1))); do echo ${envList[$i]} done return } setEnv(){ if [ -z "$1" ]; then usage; return fi case $1 in cold) FILE_TO_SOURCE=/u2/tip/conf/ctrl/lettus_cold.sh;; coles) FILE_TO_SOURCE=/u2/tip/conf/ctrl/lettus_coles.sh;; fc) FILE_TO_SOURCE=/u2/tip/conf/ctrl/lettus_fc.sh;; fcrm) FILE_TO_SOURCE=/u2/tip/conf/ctrl/lettus_fcrm.sh;; stable) FILE_TO_SOURCE=/u2/tip/conf/ctrl/lettus_stable.sh;; tip) FILE_TO_SOURCE=/u2/tip/conf/ctrl/lettus_tip.sh;; uat) FILE_TO_SOURCE=/u2/tip/conf/ctrl/lettus_uat.sh;; wellmdc) FILE_TO_SOURCE=/u2/tip/conf/ctrl/lettus_wellmdc.sh;; *) usage; return;; esac if $IS_SOURCED; then echo "Environment \"$1\" selected." echo "Now sourcing file \"$FILE_TO_SOURCE\"..." . ${FILE_TO_SOURCE} return else return 1 fi } main(){ if [ -z "$1" ]; then showEnv; return fi case $1 in -h) usage;; *) setEnv $1;; esac return } PROG="chenv" # create array of user-selectable environments envList=( cold coles fc fcrm stable tip uat wellmdc ) main "$@" return If I could, I'd like to get some feedback on a better way to accomplish any of the following: run through the case statement make script trivally simple to maintain/upgrade/update

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• I/O redirection using cygwin and mingw

  - by KLee1

  I have written a program in C and have compiled it using MinGW. When I try to run that program in Cygwin, it seems to behave normally (i.e. prints correct output etc.) However, I'm trying to pipe output to a program so that I can parse information from the program's output. However, the piping does not seem to be working in that I am not getting any input into the second program. I have confirmed this by using the following commands: This command seems to work fine: ./prog Performing this command returns nothing: ./prog | cat This command verifies the first: ./prog | wc Which returns: 0 0 0 I know that the script (including the piping from the program) works perfectly fine in an all Linux environment. Does anyone have any idea for why the piping isn't working in Cygwin? Thanks!

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• Simple C: atof giving wrong value [migrated]

  - by Doc

  I have a program that reads input from a singe line(string obviously) and organizes it into arrays. The problem I have is that at one point the program reads two different values and returns the first one twice. Initially I thought the program was reading the same value twice but when I tested it turned out that it got the correct one but is inputting the wrong one. for example Input: 2 0.90 0.75 0.7 0.65 sorry to snip it (while(fgets (string[test], sizeof(string[test]),ifp)) pch = strtok_r(NULL, " ", &prog); tem3 = atoi(pch); while (loop<tem3) { pch=strtok_r(NULL," ",&prog); venseatfloat[test][loop][DISCOUNT][OCCUPIED]=(float)atof(pch); printf("%f is discount\t",venseatfloat[test][loop][DISCOUNT][OCCUPIED]); pch=strtok_r(NULL, " ", &prog); strcpy(temp, pch); venseatfloat[test][loop][REGULAR][OCCUPIED]=(float)atof(pch); printf("%s is the string but %.3f is regular\n", temp ,venseatfloat[test][loop][DISCOUNT][OCCUPIED]); loop++; } output: >0.900000 is discount 0.75 is the string but 0.900 is regular >0.700000 is discount 0.65 is the string but 0.700 is regular What is going on?

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• Is it appropriate to set a value to a "const char *" in the header file

  - by sud

  I have seen people using 2 methods to declare and define char * Medhod-1: The header file has the below const char* COUNTRY_NAME_USA = "USA"; Medhod-2: The header file has the below declaration const char* COUNTRY_NAME_USA; The cpp file has the below defintion : const char* COUNTRY_NAME_USA = "USA"; Is method-2 wrong in some way ? What is the difference between the two ? I understand the difference between "const char * const var" , and "const char * var". If in the above methods if a "const char * const var" is declared and defined in the header as in method 1 will it make sense ?

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• how to automatically run a viruse program ?

  - by rupesh lama

  i have a c program which works as a viruse...the prof. has asked me to modify it in such a way that as soon as the pen drive (containing the prog.) is inserted in the comp. it starts executing by itself.Is it possble if any...what code(s) could be inserted in the prog. to achieve the same.

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• How to get scrolling plot in Linux (using command-line tools)?

  - by Vi

  Supposing I have a program that prints lines with data periodically, how can I turn then info them into graphical plot that updates itself each time new line available? $ ./prog 10 44 20 66 30 55 40 58 50 59 55 58 60 77 ^C $ ./prog | scrollingplot Window appears and updates on each line printed: 80| | ---- | ---- ______...__/ | / ----- | - 40| ------------------------------- 10 20 30 40 50 60 # Note that ASCII art-style plot is just for example, # I want simple X window like in mplayer. There are enough tools for static data, but I haven't seen ones for updating data (except of ksysguard).

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• Using Tkinter in python to edit the title bar

  - by Dan

  I am trying to add a custom title to a window but I am having troubles with it. I know my code isn't right but when I run it, it creates 2 windows instead, one with just the title tk and another bigger window with "Simple Prog". How do I make it so that the tk window has the title "Simple Prog" instead of having a new additional window. I dont think I'm suppose to have the Tk() part because when i have that in my complete code, there's an error from tkinter import Tk, Button, Frame, Entry, END class ABC(Frame): def __init__(self,parent=None): Frame.__init__(self,parent) self.parent = parent self.pack() ABC.make_widgets(self) def make_widgets(self): self.root = Tk() self.root.title("Simple Prog")

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